Ornamental coral pests and parasites: a biosecurity alert for aquarium trade

Pragas e parasitas de corais ornamentais: um alerta de biosseguridade para o comércio de aquariofilia

Abstract

Aquarium corals have emerged as a relevant sector not only from an economic perspective but also as a tool for ex situ conservation. However, coral pests and parasites, such as flatworms Prosthiostomum acroporae, nudibranchs Phestilla spp., parasitic copepods Tegastes acroporanus, epizoic acoelomorphs Waminoa spp., and histophagous ciliates Philaster spp., pose significant biological and economic risks in captive systems. This review synthesizes current knowledge on major pest groups affecting ornamental corals, emphasizing their life cycles, host specificity, and control strategies. Chemical treatments (e.g., levamisole, praziquantel, KCl, milbemycin, amoxicillin) show partial efficacy, yet many are limited to adult stages and risk disrupting coral microbiota. Biological control using compatible fish and invertebrates offers promise but remains underutilized. Emerging approaches, including probiotics and microbiome engineering, represent future directions for enhancing coral resilience. The aquarium environment acts as a sentinel model, often anticipating disease outbreaks later observed in wild reefs. Simple and low-cost measures, such as quarantining corals for 4 to 6 weeks, conducting visual inspections under adequate lighting, applying preventative baths, removing egg masses, and maintaining stable water quality parameters, are effective and affordable practices for reducing outbreaks in captive environments. In an era of climate change and increasing demand for captive-bred corals, integrating science-based management with aquarist practices is essential. Preventive measures, rapid diagnostics, and biotechnological innovation will be key to ensuring coral health and advancing the aquarium hobby as a tool for marine conservation.

Keywords:
coral health; ornamental aquaculture; coral pests; biosecurity

Resumo

Os corais ornamentais de aquário tornaram-se um setor relevante não apenas economicamente, mas também como ferramenta de conservação ex situ. No entanto, pragas e parasitas como os platelmintos Prosthiostomum acroporae, nudibrânquios Phestilla spp., copépodes parasitas Tegastes acroporanus, acoelomorfos epizoicos Waminoa spp. e ciliados histófagos Philaster spp. representam riscos biológicos e econômicos significativos em sistemas cativos. Esta revisão sintetiza o conhecimento atual sobre os principais grupos de pragas que afetam corais ornamentais, com ênfase em seus ciclos de vida, especificidade ao hospedeiro e estratégias de controle. Tratamentos químicos (como levamisol, praziquantel, KCl, milbemicina e amoxicilina) apresentam eficácia parcial, sendo geralmente limitados às fases adultas e com risco de desequilíbrio da microbiota dos corais. O controle biológico com peixes e invertebrados compatíveis mostra potencial, mas é pouco explorado. Estratégias emergentes, como o uso de probióticos e a engenharia do microbioma, representam direções promissoras para aumentar a resiliência dos corais. O ambiente de aquário funciona como um modelo sentinela, frequentemente antecipando surtos de doenças que mais tarde são observados em recifes naturais. Medidas simples e de baixo custo, como quarentena de corais por 4 a 6 semanas, realizar inspeções visuais sob iluminação adequada, aplicar banhos preventivos, remover massas de ovos e manter parâmetros estáveis de qualidade da água, são práticas eficazes e acessíveis para reduzir surtos em ambientes cativeiro. Em um cenário de mudanças climáticas e crescente demanda por corais cultivados em cativeiro, é essencial integrar a gestão científica com práticas de aquaristas. Medidas preventivas, diagnóstico rápido e inovação biotecnológica serão fundamentais para garantir a saúde dos corais e fortalecer o aquarismo como ferramenta de conservação marinha.

Palavras-chave:
saúde de corais; aquicultura ornamental; pestes de corais; biosseguridade

1. Introduction

Aquarium corals have emerged as a relevant sector not only from an economic perspective but also as a tool for ex situ conservation, enabling the maintenance of species threatened by the degradation of natural reefs due to climate change, pollution, and mass bleaching events (Lesser et al., 2013; Baker et al., 2018).

In addition to their intrinsic ecological value, corals and their symbiotic organisms constitute one of the largest marine sources of bioactive metabolites with pharmaceutical and biotechnological potential. Recent studies have demonstrated that endophytic microorganisms associated with algae and corals, particularly Actinobacteria of the genus Streptomyces, are capable of producing compounds with antimicrobial, antiviral, anticancer, and antioxidant activities, reinforcing the importance of conserving these organisms as reservoirs of functional biodiversity (El-Gendy et al., 2022; Abdel-Tawab et al., 2024; Osman et al., 2025).

In order to maintain at-risk species in controlled systems, the aquarium hobby may indirectly contribute to the preservation of potential future therapeutic resources. Consequently, ornamental aquaculture practices have the potential to reduce harvesting pressure on wild populations, provided they are accompanied by rigorous biosecurity protocols and disease prevention measures (Leal et al., 2016; Sheridan et al., 2013).

The international trade of ornamental corals is regulated under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which provides a multilateral framework to ensure that such activities do not threaten the survival of species in the wild (Cites, 2024). All reef-building corals (Order Scleractinia), fire corals (Milleporidae), lace corals (Stylasteridae), blue corals (Heliopora coerulea; more recently reflected as Helioporidae spp. in Parties’ consolidated lists), and black corals (Antipatharia) are listed in Cites (2024) Appendix II. Under Article IV of the Convention, international trade in Appendix-II specimens requires prior issuance of an export permit based on a non-detriment finding by the national Scientific Authority.

While the ornamental coral trade supports biodiversity appreciation and reef restoration, it also presents biosecurity risks due to the inadvertent spread of harmful organisms. In this context, it is important to differentiate between pests and parasites, terms often used interchangeably but which describe distinct biological interactions. Scientifically, parasites are organisms that establish a close and often prolonged association with their host, from which they extract nutrients, usually without immediate lethality (Barton et al., 2020a). In contrast, pests are defined in applied ecology as any organism, parasitic or not, that causes damage, loss, or is considered undesirable in a specific context (Mound et al., 2022), such as coral aquaculture. Management approaches also differ: organisms that behave as true parasites (i.e., intimate, persistent host associations) may require targeted chemotherapeutants and staged treatment regimes, whereas many context-dependent ‘pests’ in coral aquaculture are mitigated through short-term prophylactic dips/baths and/or biological control, integrated into quarantine workflows to reduce cross-system transfer. Recognizing these distinctions strengthens biosecurity, quarantine design, and targeted interventions in trade systems (Barton et al., 2020a, b).

Organisms such as corallivorous flatworms (Figure 1) Prosthiostomum acroporae Rawlinson, Gillis, Billings & Borneman, 2011, nudibranchs of the genus Phestilla Bergh, 1874, including Phestilla subodiosus Wang, Conti-Jerpe, Richards & Baker, 2020 (Figure 2A), P. goniophaga Gohar & Soliman, 1967 (Figure 2B), and P. sibogae Bergh, 1905, parasitic copepods Tegastes acroporanus Humes, 1981 (Figure 3), epizoic acoelans Waminoa spp Gruber, 1888 (Figure 4), and histophagous ciliates Philaster lucinda Norén, Moestrup & Rehnstam-Holm, 1999 (Figure 5A) and Philaster guamensis Lobban, Raymundo & Montagnes, 2011 (Figure 5B) can cause severe impacts on ornamental corals, resulting in tissue loss, rapid necrosis, reduced growth, and even mortality (Rawlinson and Stella, 2012; Wang et al., 2020; Christie and Raines, 2016; Kunihiro et al., 2019; Ravindran et al., 2022).

Figure 1
Adult flatworm (black arrowheads) at the base of a coral of the genus Euphyllia. Photo by Pedro Henrique Magalhães Cardoso (Brazil).

Figure 2
(A) Montipora spp. parasitized by Phestilla subodiosus (black arrowheads). The inset (A) shows the parasite under a stereomicroscope (40x); (B) Goniopora spp. (white arrow head) parasitized by Phestilla goniophaga (black arrow heads). Photo by Pedro Henrique Magalhães Cardoso (Brazil).

Figure 3
Tegastes acroporanus (commonly known as red bugs) infesting Acropora corals. This copepod measures approximately 1 mm in length and requires magnification for proper visualization. Note the distinct red pigmentation of the urosome (a) in contrast to the bright yellow prosome (b) and the morphology of the maxillipeds (c), which are characteristic of the species. Source: Christie and Raines (2016).

Figure 4
Flatworms of the genus Waminoa (black arrowheads) on (A) Euphyllia and (B) Goniopora corals. Photo by Pedro Henrique Magalhães Cardoso (Brazil).

Figure 5
Histophagous ciliates observed in coral infections: (A) Philaster lucinda and (B) Philaster guamensis, opportunistic protozoans that feed directly on coral tissue. These species have been associated with severe coral syndromes, including Brown Jelly Syndrome (BJS), characterized by rapid tissue necrosis and partial or total colony mortality. Source: Coral RTN (2025).

In this context, it becomes essential to review the current state of knowledge on the most common and impactful parasites and pests affecting ornamental corals, particularly those frequently encountered in the aquarium trade. Although a wide range of specialized parasitic taxa occur in nature, this review is specifically centered on the pests and parasites groups most frequently documented in ornamental aquaculture and aquarium hobbyist settings. These include flatworms, nudibranchs, copepods, epizoic acoelomorphs, and histophagous ciliates. The discussion highlights recent advances in diagnosis, prevention, and control, as well as emerging trends such as probiotics and microbiome engineering (Peixoto et al., 2021; Thatcher et al., 2022; Pribawastuti et al., 2024; Thurber et al., 2025). Therefore, the aim of this review is to compile and critically discuss the available knowledge on parasites and pests affecting ornamental corals, addressing their biological and economic impacts, as well as strategies for prevention, control, and biotechnological innovations applicable to the aquarium hobby and aquaculture, with a view to supporting more sustainable and conservation-oriented practices.

2. Scope of Review

The present review was conducted through a structured search of the scientific literature in databases including Web of Science, Scopus, PubMed, and Google Scholar. The following descriptors were used, either individually or in combination with Boolean operators (“AND”, “OR”): “ornamental corals”, “aquarium corals”, “coral pests”, “coral parasites”, “coral diseases”, “flatworms”, “Waminoa”, “Prosthiostomum acroporae”, “nudibranchs”, “Phestilla”, “copepods”, “Tegastes acroporanus”, “ciliates”, “Philaster”, “coral biosecurity”, “quarantine protocols”, “chemical treatments”, “coral dips”, “biological control”, “Chelidonura varians”, “probiotics”, “Beneficial Microorganisms for Corals”, “BMCs”, “microbiome engineering”, and “coral microbiome”. Preference was given to peer-reviewed articles published between 2000 and 2025, with additional inclusion of relevant technical reports and gray literature when necessary to contextualize ornamental aquarium practices. This strategy ensured the inclusion of classical studies on coral pests (e.g., Waminoa, Phestilla, Tegastes, ciliates) as well as emerging research on biological control and microbiome-based interventions.

Some of the photographic records included in this review were obtained directly by the author in ornamental coral imports in Brazil, providing original documentation of pests and parasites in the national context.

3. Main Groups of Parasites and Pests in Corals

3.1. Corallivorous flatworms (Acropora eating flatworms – AEFW and Euphyllia eating flatworms – EEFW)

Flatworm species such as P. acroporae, which parasitize corals of the genus Acropora (Barton et al., 2019; Wang et al., 2020), and other eating flatworms (EFWs) not yet formally described, such as those affecting Euphyllia species, can cause rapid tissue necrosis in the affected colonies, representing one of the most feared pests in coral aquarium hobby (Barton et al., 2019). Flatworms on corals are often difficult to detect with the naked eye. However, mortality in Acropora colonies or persistent polyp retraction in Euphyllia should raise suspicion of their presence. In Acropora and Euphyllia colonies, adult worms are commonly observed attached to the coral base (Figure 1), and egg masses (Figure 6), visible to the naked eye are frequently present, aiding in early detection (personal communication).

Figure 6
(A) Eggs (black arrowheads) of AEFW (Acropora-eating flatworm) on corals of the genus Acropora; (B) eggs (black arrowheads) of EEFW (Euphyllia-eating flatworm) on corals of the genus Euphyllia. Photo by Pedro Henrique Magalhães Cardoso (Brazil).

The life cycle of the Acropora Eating Flatworm (P. acroporae) (Figure 7) begins with the deposition of egg masses on the exposed skeleton of Acropora colonies. The incubation period is temperature-dependent: approximately 26 days at 21 °C, 15 days at 24 °C, 11 days at 27 °C, and only 9 days at 30 °C. Upon hatching, juveniles emerge already metamorphosed and capable of locomotion, which enables their dispersal only among closely positioned colonies. Sexual maturity is reached in approximately 35 days at 27 °C, with an average life cycle duration of 38 days, varying from 36 to 64 days depending on temperature. Warmer environments accelerate development, increase hatching rates, and result in larger adults, factors that explain the higher frequency and severity of outbreaks in aquaculture systems maintained at elevated temperatures (Barton et al., 2019).

Figure 7
Life cycle of Prosthiostomum acroporae; from Barton et al. (2019).

Nevertheless, treatment remains a significant challenge, as most chemical approaches show limited efficacy against egg stages and primarily target adults. As a result, multiple applications are required at intervals consistent with the parasite's life cycle (Barton et al., 2019). Therefore, preventive measures remain essential, including thorough visual inspection, mechanical removal of egg masses, and the application of weekly chemical dips (e.g., levamisole, praziquantel) for a minimum of five treatments to encompass the full parasite cycle. These measures have shown efficacy rates exceeding 90% against adult flatworms (Barton et al., 2021).

Despite the limited availability of peer-reviewed studies supporting the use of potassium chloride (KCl) against a broad range of coral-associated pests, brief immersion treatments using 1–2% KCl solutions are widely adopted in aquarium husbandry to promote the detachment of soft-bodied organisms, including flatworms. For this reason, this approach is depicted in Figure 8 as a commonly applied practical measure (personal communication).

Figure 8
Illustrative example of a short-duration potassium chloride (KCl) dip (1%) applied as a supportive husbandry measure to facilitate flatworm removal from a Euphyllia coral. This approach is also commonly employed in aquarium practice to assist in the detachment of other soft-bodied coral-associated organisms, including histophagous ciliates and nudibranchs. Photo by Pedro Henrique Magalhães Cardoso (Brazil).

3.2. Corallivorous nudibranchs

Nudibranch species of the genus Phestilla have evolved to specialize on distinct coral hosts. Montipora corals are parasitized by P. subodiosus (Figure 2A), Goniopora by P. goniophaga (Figure 2B), and Porites by P. sibogae (Hu et al., 2020; Wang et al., 2020; Gochfeld and Aeby, 1997). In aquarium systems, these nudibranchs can cause rapid mortality of their coral hosts due to the absence of natural predators, whereas in natural reef environments they are generally kept under control by wrasses and certain crab species (Gochfeld and Aeby, 1997).

Chemical control of these parasites is considered challenging, as most tested compounds have shown low efficacy or have induced adverse effects on the host corals. In aquarium practice, however, short-duration baths in potassium chloride (KCl) at concentrations around 2% for 10 min are also commonly employed for the removal of adult nudibranchs. This method has shown effectiveness in dislodging soft-bodied individuals from coral surfaces without causing apparent harm to the coral host. Nevertheless, it does not affect nudibranch egg masses, requiring repeated weekly applications aligned with the life cycle of the parasite to minimize reinfestation.

In natural reef systems, biological control is primarily carried out by labrid fishes (Figure 9), and controlled introduction of such predators in captive systems has shown promise as part of an integrated pest management approach (Barton et al., 2020b). When combined with visual inspections and quarantine protocols, this strategy can contribute to effective long-term control.

Figure 9
(A) Halichoeres melanurus and (B) Coris gaimard used in the aquarium hobby as biological control agents for natural pest management in coral systems. Photo by Pedro Henrique Magalhães Cardoso (Brazil).

Recent studies underscore the ecological complexity of coral-gastropod interactions. Research conducted in the Gulf of Thailand documented 13 gastropod species associated with corals, including nine Phestilla species and four epitoniids, as well as the description of a new species, Phestilla arnoldi, found exclusively on Acropora muricata (Mehrotra et al., 2024). These findings expand our understanding of corallivore diversity and highlight the difficulty in classifying such organisms strictly as parasites or predators, as some species may partially or entirely consume their hosts, implications that are significant for reef health and resilience.

3.3. Parasitic copepods (“Red bugs”)

Tegastes acroporanus is a parasitic copepod that exclusively infests Acropora colonies, adhering primarily to the polyps and superficial tissues of the coral (Figure 3). Its presence is associated with gradual loss of coloration, persistent polyp retraction, and a marked reduction in coral growth and calcification, factors that compromise both the ornamental appeal and physiological viability of the host (Christie and Raines, 2016). In severe outbreaks, increased mucus production and secondary susceptibility to opportunistic pathogens may also be observed.

Studies involving weekly immersion treatments with high concentrations of milbemycin oxime (0.032 ppm) have demonstrated both efficacy and coral tolerance when applied to arthropod-infested corals, without observable adverse effects on the host (Krol et al., 2023). These findings suggest that repeated immersion treatments may represent a viable option for managing T. acroporanus infestations. However, such treatments should be implemented with strict monitoring and judicious use to minimize unintended impacts on beneficial microfauna.

In parallel, biological control via labrid fishes, which naturally prey on small invertebrates in reef environments, has also shown promise under captive conditions, supporting integrated management strategies based on visual inspection, quarantine protocols, and preventative measures (Barton et al., 2020b).

3.4. Epizoic acoelomorphs (Waminoa spp.)

Although initially considered commensals, recent studies have demonstrated that Waminoa spp. exert a dual negative impact on corals. On one hand, they directly compete for zooplankton in the water column, thereby reducing the availability of food for the coral host. On the other hand, their persistent presence on the coral surface (Figure 4) causes shading, which decreases the photosynthetic efficiency of the symbiotic zooxanthellae and compromises host physiology (Wijgerde et al., 2011). Recent molecular evidence further indicates that corals infested by Waminoa show altered expression of immune- and stress-response genes, suggesting that these acoelomorphs impose a chronic physiological burden on their hosts (Maggioni et al., 2022). Global records also indicate an underestimated diversity of morphotypes, with distinct lineages capable of direct transmission between neighboring colonies (Kunihiro et al., 2019; Hoeksema and Farenzena, 2012).

In ornamental aquaria, Waminoa infestations are considered recurrent and difficult to eradicate. Prevention relies on meticulous inspection and strict quarantine of newly introduced colonies, often requiring observation under a stereomicroscope, since eggs and juveniles are difficult to detect visually. While commercial dips based on plant extracts may show some efficacy against adults, they do not eliminate eggs, requiring repeated applications at 7-10 day intervals. Biological control using nudibranchs of the genus Chelidonura, reported as natural predators, has been applied with relative success but presents practical limitations in terms of handling and availability (Fenner, 2002). Thus, preventive measures and integrated management, including quarantine protocols, periodic dips, and, where feasible, biological control, remain the most recommended strategies to minimize the spread of these acoelomorphs in ornamental aquaculture systems.

3.5. Histophagous ciliates

Histophagous ciliates are opportunistic protozoans that feed directly on coral tissue, colonizing the surface or already-damaged areas of the host. Species such as Philaster lucinda (Figure 5A) and Philaster guamensis (Figure 5B) have been associated with devastating coral syndromes, such as Brown Jelly Syndrome (BJS), characterized by rapid tissue necrosis and partial or total colony mortality (Cheng et al., 2021; Ravindran et al., 2022). The direct action of these ciliates results in rapid tissue degradation, polyp retraction, and exposure of the coral skeleton. Experimental studies further confirm that these ciliates can cause mortality in various coral species within less than 72 h (Ding et al., 2022), reinforcing their role as primary disease agents and highlighting the urgent need for prevention protocols, rapid diagnosis, and immediate control measures.

In addition to mechanical and histophagous damage, there is growing evidence that their presence facilitates secondary colonization by opportunistic bacteria, accelerating necrosis and impairing the coral’s immune response (Ding et al., 2022). This synergistic interaction between ciliates and bacteria has been proposed as a key factor explaining the rapid progression of lesions observed both in aquaria and in natural reef environments.

Pharmacological trials have shown that immersion in 1.5% potassium chloride (KCl) solutions may be effective against these protozoans without inducing significant adverse effects in host corals, whereas hydrogen peroxide (H₂O₂) treatments are associated with marked stress responses (e.g., polyp contraction) and are therefore not recommended (Cheng et al., 2021).

More recently, natural botanicals such as extracts of Melia toosendan have been tested as eco-friendly alternatives, with concentrations around 2500 ppm proving effective in eliminating ciliates while minimizing coral stress responses, showing promise for application in large-scale aquaculture and reef restoration (Ding et al., 2025). The application of clove oil extract effectively eradicated histophagous ciliates in corals within a short exposure period of 10 min, while maintaining the integrity of zooxanthellae, chlorophyll a levels, and antioxidant enzyme activity (Chu et al., 2022).

4. Preventive and Control Strategies in Ornamental Coral Aquaculture

4.1. Prevention and biosecurity

Prevention remains the most effective strategy for avoiding the introduction of pests and parasites into ornamental aquaculture and reef aquarium systems. Quarantine protocols and visual inspections are essential, as early detection significantly reduces both costs and mortality (Borneman, 2008; Sheridan et al., 2013). The literature emphasizes that newly acquired coral colonies should be kept in isolation for a minimum of 4-6 weeks, with periodic monitoring under a stereomicroscope, before being introduced into main display or production tanks (Leal et al., 2016).

Another key preventive measure is the maintenance of stable physicochemical parameters (e.g., temperature, salinity, nutrient levels), as environmental stress increases coral susceptibility to bacterial and protozoan infections (Sweet and Séré, 2016; Montano et al., 2015). The integration of biosecurity practices, such as the use of UV sterilization, ozonation, microbiological water monitoring, and reduced stocking density, has proven effective in commercial aquaculture systems (Sheridan et al., 2013).

4.2. Chemical dips and treatments

A variety of short-duration prophylactic dips have been tested for their efficacy against coral pests and parasites. The use of levamisole and praziquantel has demonstrated high effectiveness against corallivorous flatworms (Prosthiostomum acroporae), with >90% removal of adult individuals and no adverse effects on treated coral fragments (Barton et al., 2021).

In cases of ciliate infection (Philaster lucinda), potassium chloride (KCl 1.5%) has proven to be an effective and safe treatment, whereas hydrogen peroxide induces severe polyp stress and is not recommended (Cheng et al., 2021). In that study, 1.5% KCl showed a rapid lethal effect on ciliates, improving coral survival while avoiding polyp atrophy, and the authors discuss osmotic-pressure regulation as a plausible mechanism underlying its antiparasitic action. Cheng et al. (2021) further note that KCl is widely used in the food industry as a NaCl substitute and cite prior reports indicating bacteriostatic activity against multiple bacterial taxa, reinforcing that KCl exposure can exert broad inhibitory pressure on microorganisms without necessarily compromising coral tissue integrity at the tested concentration. Although peer-reviewed evidence remains comparatively scarce for KCl against other coral-associated pests, short-duration KCl dips at 1-2% are commonly used in aquarium practice to facilitate the removal of soft-bodied organisms, including flatworms (Figure 8) and nudibranchs, and are generally regarded as well tolerated by corals.

Commercial products containing plant-based extracts, such as Coral Rx™, Revive™, and Melafix™, have been used with partial efficacy against flatworms. For instance, Melafix™ Marine, when applied as short-term dips, has demonstrated the ability to kill parasitic flatworms on live rock and corals, and consistent weekly applications reportedly eliminate infestations within several weeks (API, Melafix Marine Technical Sheet; user reports). Coral Rx™, formulated with natural extracts and independently tested, is marketed as effective in removing hard-to-control pests like Acropora-eating flatworms, without harming the corals (Coral Rx product documentation). Non-experimental reports with Revive™ also suggest pest-reducing action, although its effectiveness appears variable and largely confined to adult flatworms (Reef2Reef, 2020; API Fishcare, 2025; Reef Cleaners, 2025).

4.3. Biological control

The use of natural predators represents a promising alternative to chemical treatments. Controlled trials have shown that the wrasse Pseudocheilinus hexataenia successfully removed 100% of adult flatworms within 24 h, while the shrimp Lysmata vittata consumed up to 82% of adult P. acroporae and 64% of their eggs (Barton et al., 2020b). In addition, labrid fishes commonly used in the aquarium hobby, such as Halichoeres melanurus (Figure 9A) and Coris gaimard (Figure 9B), are frequently reported as effective biological controllers of flatworms in coral systems. Similarly, the nudibranch Chelidonura varians has been reported as an efficient predator of epizoic flatworms (Waminoa spp.), although its large-scale application still lacks standardization (Fenner, 2002).

Despite their potential, biological control agents present management challenges in aquaculture settings, such as host species compatibility and the risk of non-selective predation. Therefore, their use is best integrated into broader quarantine protocols and chemical dip treatments as part of an integrated pest management (IPM) strategy.

4.4. Conventional pharmacological therapies

The use of pharmacological therapies in corals remains a sensitive and debated topic; however, some trials have demonstrated efficacy in specific contexts. Among antiparasitic agents, milbemycin oxime has proven highly effective against the copepod Tegastes acroporanus, successfully eliminating infestations in closed systems after multiple treatments, although with collateral impacts on associated microfauna, including non-target small crustaceans (Christie and Raines, 2016; Krol et al., 2023).

In the case of bacterial infections, particularly in field settings, topical antibiotics have been employed. Amoxicillin in paste form has been used to treat Stony Coral Tissue Loss Disease (SCTLD), achieving success rates exceeding 90% in ex situ applications (Pelose et al., 2024).

Nevertheless, studies have also warned of the risks associated with such interventions, including the development of bacterial resistance, disruption of coral-associated microbiota, and broader environmental impacts (Ushijima et al., 2020; Vega Thurber et al., 2025). As such, chemical treatments, whether antiparasitic or antibiotic, should be reserved for severe cases, applied under strict monitoring, and always integrated with preventive strategies such as quarantine and biosecurity protocols.

4.5. Probiotics and microbiome-based innovations for coral health

In recent years, interest has grown in the use of probiotics and coral microbiome engineering as sustainable alternatives for disease prevention and resilience enhancement. Studies have demonstrated that selected bacterial consortia (e.g., Halomonas, Pseudoalteromonas) can reduce mortality caused by Vibrio coralliilyticus and increase thermal tolerance in corals (Peixoto et al., 2021; Thatcher et al., 2022). This strategy has been referred to as Beneficial Microorganisms for Corals (BMCs), with potential applications in both ornamental aquaristics and reef restoration programs (Peixoto et al., 2021).

Recent experiments further demonstrated that BMC application prevented mortality of thermally sensitive coral species during short-term heat stress, maintaining photophysiological performance and underscoring the potential of rapid deployment prior to heatwave events (de Breuyn et al., 2025).

Another innovative approach is microbiome engineering, which aims to manipulate coral-associated microbial communities through directed inoculation, artificial biofilms, and supplementation with stress-resistant symbionts (Pribawastuti et al., 2024; Thurber et al., 2025). Probiotics have also been shown to induce beneficial restructuring of microbiomes in coral-associated fishes, highlighting indirect ecosystem-level effects and reinforcing the One Health perspective in reef conservation (Rosado et al., 2025).

However, results are not universally positive: in early coral recruits, exposure to the probiotic strain Pseudoalteromonas sp. McH1-7 did not significantly enhance survival under stony coral tissue loss disease (SCTLD) challenges, suggesting that life stage, disease context, and experimental conditions critically shape outcomes (Demko et al., 2025).

Although still experimental, this approach represents a shift from traditional “pest treatment” paradigms toward strengthening the coral holobiont as a whole.

5. Discussion

The data reviewed herein demonstrate that many coral pests, parasites and associated diseases initially described in ornamental aquaria have clear parallels in natural reef environments, albeit with varying intensities. The Acropora-eating flatworms (AEFW), for example, were first recognized as a devastating pest in captive systems before being confirmed in wild reefs (Rawlinson and Stella, 2012). A similar trend is observed with histophagous ciliates such as Philaster lucinda, which, although opportunistic in natural settings, act as primary pathogens in closed systems (Cheng et al., 2021; Ding et al., 2022). These patterns suggest that aquariums may serve as sentinel models, anticipating outbreaks that may later be recognized in reef ecosystems.

Often viewed solely as a recreational or commercial activity, coral aquarium hobby has in fact provided valuable empirical insights into pest emergence and treatment efficacy (Sweet et al., 2012; Barton et al., 2020b). Species such as Phestilla subodiosus were informally recognized by aquarium hobbyists before being formally described in the scientific literature in 2020 (Wang et al., 2020), and conservation protocols currently used, such as chemical dips and topical antibiotics, originated from practices adapted by aquarists (Christie and Raines, 2016; Pelose et al., 2024). This integration between hobbyist observation and scientific research not only strengthens ornamental coral management but may also accelerate responses to emerging epizootics in the field, such as the stony coral tissue loss disease in the Caribbean.

Recent studies suggest that climate change and eutrophication may intensify parasitic interactions within the coral holobiont itself. Under thermal stress, Symbiodinium symbionts can shift from mutualists to parasites, retaining more carbon and reducing translocation to the coral host (Lesser et al., 2013; Baker et al., 2018). Likewise, epizoic organisms such as Waminoa spp. proliferate under stressful conditions, exacerbating coral mortality (Hoeksema and Farenzena, 2012; Kunihiro et al., 2019).

In addition, recent research has expanded our understanding of other parasitic interactions in corals. Corallivorous polychaetes such as fireworms (Hermodice carunculata) have been identified as potential reservoirs and vectors of corallicolid apicomplexans, transmitting these parasites via feces and representing a relevant route of spread in reef systems (Bonacolta et al., 2025). Similarly, endoparasitic crustaceans of the order Ascothoracida exhibit diverse trophic strategies, ranging from direct tissue consumption to nutrient theft from the coral digestive tract, highlighting that parasitism can take multiple physiologically damaging forms (Zalota et al., 2025). These findings reveal that coral parasitism is more diverse and complex than traditionally recognized, with synergistic interactions alongside environmental stressors accelerating degradation processes (Bonacolta et al., 2025; Zalota et al., 2025).

In the past five years, there has also been a notable increase in pest and parasite occurrence in corals used in aquarium hobby, particularly those farmed in natural environments. While part of this phenomenon may be linked to climate change, an important contributing factor is the dissemination of information through forums and specialized networks, which has enabled earlier detection and more efficient management of these organisms. This exchange of experiences between aquarists and experts has significantly reduced coral mortality in controlled systems. However, despite its practical relevance, this topic remains underexplored in academic circles and is virtually absent from the Brazilian scientific literature, highlighting the urgent need to integrate empirical observations with systematic research.

Although progress has been made with the use of dips (e.g., levamisole, praziquantel, KCl, milbemycin) and topical antibiotics (e.g., amoxicillin), several challenges remain. Many treatments are effective only against adult stages and fail to eliminate eggs, necessitating repeated protocols and extended quarantine periods (Barton et al., 2021). Additionally, the use of antibiotics carries the risk of microbial resistance and disruption of the coral microbiome (Ushijima et al., 2020; Thurber et al., 2025). Therefore, current methods should be regarded more as palliative interventions than definitive solutions.

The future of ornamental coral pest and parasite disease management points toward preventive and holistic approaches. The use of probiotics, specifically Beneficial Microorganisms for Corals (BMCs), has already shown promising results in experimental trials, with improved thermal tolerance and reduced mortality from Vibrio infections (Peixoto et al., 2021; Thatcher et al., 2022). Another emerging frontier is microbiome engineering, which aims to manipulate microbial communities to provide long-term resilience to the coral host (Pribawastuti et al., 2024).

In parallel, the implementation of biological control strategies using compatible fish and crustaceans may reduce the reliance on chemical treatments in aquaculture (Barton et al., 2020b), while rapid diagnostic tools, such as molecular assays for Vibrio coralliilyticus (Ushijima et al., 2020) and artificial intelligence applications (Selwyn et al., 2024), are expected to revolutionize early outbreak detection.

The outlook for the next decade is not merely to eliminate pests, but to enhance coral holobiont resilience by integrating prevention, biotechnology, and high-resolution monitoring tools.

6. Conclusion

Ornamental coral parasites and pests represent a multifaceted challenge with implications for trade, aquaculture, and the conservation of natural reef ecosystems. This review highlights that:

1. Aquariums function as anticipatory models, often revealing pests and syndromes prior to their detection in the wild.

2. Prevention through quarantine and biosecurity remains the most effective strategy, given the current limitations of available treatments.

3. Integration between scientific knowledge and aquarist practices is essential for advancing management strategies.

4. Future frontiers lie in probiotics, microbiome engineering, biological control, and rapid diagnostics, which have the potential to transform coral health in both aquaria and reef systems.

In the context of climate change and increasing demand for captive-bred ornamental corals, the implementation of preventive and innovative protocols will be crucial, not only to ensure the well being of corals in captivity but also to uphold the sustainability of ornamental aquaculture and coral aquarium hobby as a legitimate tool for marine conservation. To support this goal, coral traders and hobbyists can adopt practical low-cost techniques such as quarantining new coral specimens for at least 4-6 weeks, inspecting them under proper lighting for signs of pests, applying routine coral dips with commercial products, manually removing visible egg masses, and maintaining stable water quality parameters. These simple steps, when applied consistently, can significantly reduce pest and parasite outbreaks and enhance coral health in captive environments.

Acknowledgments

We acknowledge the National Council for Scientific and Technological Development (CNPq) for providing research grants to A. M. Moreno (CNPq #312684/2022-3) and M. L. Martins (CNPq #303822/2022-8), and the Coordination for the Improvement of Higher Education Personnel (CAPES) for providing research grants to Pedro H. M. Cardoso (CAPES #88887.078833/2024-00). We also thank Kiuslei Cassiolato Peixes Company for granting access to facilities, which enabled the photographic documentation of ornamental corals and pests in Brazil. All photographs credited to Pedro Henrique Magalhães Cardoso derive from the author’s own fieldwork and professional experience, underscoring the originality of this contribution.

• Data Availability Statement
  All data supporting the findings of this study are fully presented within the manuscript. Additional information can be provided by the corresponding author upon reasonable request.

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Edited by

• Editor:
  Takako Matsumura Tundisi

Data availability

All data supporting the findings of this study are fully presented within the manuscript. Additional information can be provided by the corresponding author upon reasonable request.

Publication Dates

• Publication in this collection
  16 Mar 2026
• Date of issue
  2026

History

• Received
  03 Dec 2025
• Accepted
  29 Jan 2026